#include<stdio.h>
#include<math.h>
#include<stdlib.h>
int main(){

    freopen("triangle.in","r",stdin);

    double a,b,c;
    double area;
    double s;

    while(3==scanf("%lf%lf%lf",&a,&b,&c)){

        s=a+b+c;
        area=sqrt(s*(s-a)*(s-b)*(s-c));

        printf("%.3f\n",area);
    }

    return 0;
}
